Adjustable rotation radius articulated joint for gym machines and knee tutors

ABSTRACT

This invention can be profitably employed in the fields of medicine and sports in the machines used to strengthen the muscles of the knee and in knee tutors.  
     In its simplest version, the articulated joint is formed by two plates ( 1, 2 ) which can move freely on one another; alternatively, one plate ( 1 ) or the other ( 2 ) can be fastened to a fixed structure by means of a fastener. One of the plates features two openings ( 2.2, 2.3 ), where the first ( 2.2 ) is located at the center of a plate and is shaped like a rectangle. The second opening ( 2.3 ) has a specific shape: at first it is a circumference whose radius is equal to “I”; subsequently, it is a spiral which returns towards the center of the plate ( 2 ).  
     The other plate features two pins ( 1.2  and  1.3 ), located at a distance “I”; the first pin ( 1.2 ) is located in the central position and is inserted into opening the ( 2.2 ); the second pin ( 1.3 ) is in a peripheral position and is located in the second opening ( 2.3 ).  
     Alternatively the plate ( 2 ) can be replaced by several overlapping plates ( 3, 4, 5, 6, 7 ); the semi-plates are arranged in overlapping couples ( 4, 7  and  5, 6 ). The semi-plates ( 4, 7 ) are fastened to the plate ( 3 ) by means of a pin ( 4.1 ) placed in an ideal point of rotation ( 11 ) and are therefore free to rotate onto the semi-plates ( 5, 6 ).

TECHNICAL FIELD

[0001] This invention can be profitably employed in the fields ofmedicine and sports as it is an indispensable component of knee tutorsand of machines used to strengthen or in rehabilitation to restore themuscles of the knee to their former healthy condition.

[0002] The knee is the intermediate articulation of the lower limbs. Themovement whereby the knee is extended, or rather, the movement ofextending the leg from the thigh is performed by means of the quadricepmuscle, which is inserted in the foretuberosity of the tibia, a coupleof centimeters below the knee. The movement of bending the knee, that isto say the movement of flexing the leg from the thigh is performed bymeans of the hind muscles of the thigh, as illustrated in FIG. 1. Theflex/extension movement is always executed at the fore-hind level.

[0003] The articular surfaces that come into contact in the knee are thefemoral condyles (the distal, i.e. farther, part of the femur), and thetibia plate (the proximal, i.e. closer, part of the tibia), asillustrated in FIG. 2. The femoral condyles consist in round surfaceswith a bending radius which is rather narrow but which varies; indeedtheir profile is very similar to a spiral. The tibia plate, or ratherthe glenoid cavity of the tibia, has a much wider bending radius thanthe femoral condyles.

[0004] The articular mechanics of the knee is therefore complex, and thetype of movement that is made is in direct relation to the angle atwhich the knee is open. Let us consider an extended leg to be thestarting point at a 0 angle. In the first 20-25° of the bend (i.e.: theangle of ordinary walking) the articulation's mechanics entails a sheerrotation between the two articular surfaces: each point of the femoralcondyles is in contact with a corresponding point on the tibia plate. Ifthe flexing continues, in the subsequent 110-115°, approximately, thereis a combined sliding and rotating movement (of the tibia with referenceto the femur). In particular, a rotation and a sliding movement occur;as the leg flexes the sliding movement gradually progresses endeventually prevails over the over the rotation when a sheer slidingmovement occurs: the femoral condyles slide without rotating on thetibia plate. The knee's ligaments withhold the articular caps duringthese sliding movements and ensure the knee's fore-hind stability,enabling the execution of hinge movements whereby the articular surfacesremain in contact.

[0005] Thus, in the flex/extension mechanics of the knee there is nofixed center of rotation. When the leg is flexed (starting from anextended position), in the first 20° there is a center of rotationlocated 60 mm away from the tibia's articular surface. However, as thebending movement continues, the point of rotation moves on and, at thesame time, the radius grows narrower, until it reaches a minimumdistance of approximately 12 mm from the tibia (as can be seen in FIG.2).

[0006] This variation in the radius is transformed into a variation inthe distance between a point located in the center of the femoralcondyle (which has been identified by tests in the first 20-25° of theflex/extension) and another point situated on the external malleolus.Indeed, by measuring this distance, experiments reveal that in extendingfrom 135° (position A), to 0° (position B), it can increase from 15 to40 mm (distance R_(B)-R_(A)), as can be seen in FIG. 3. The scale of thevariation depends on the conformation of the knee in question.

[0007] With reference to physiotherapeutic or rehabilitation problems,when it is necessary to support and follow the knee in its movements,one usually resorts to particular mechanical devices which are strappedto the thigh and leg by means of a system of belts (a sling) and whichguide the articulation in its movements.

[0008] These devices are used in knee tutors, in the machines used forpassive gymnastics, and in the weight-lifting machines for specificmuscles known as leg curl and leg extension machines.

[0009] These mechanical devices, which are thus bound to the limb, arehinged to an articulated joint which generally has a fixed center ofrotation and which therefore is unable to provide the combined slidingand rotating movements and change the center of rotation, therebyproducing anomalous tensions. The latter are caused by the differenttrajectories of the articulated joint's mechanical devices (circle arc)compared to the one theoretically accomplished by the leg (spiral arc).Indeed, as previously described, the leg reduces its radius when itflexes (the above mentioned R_(B)-R_(A)); this causes the mechanicaldevice to rub against the leg, bringing about a friction which is passedon to the belts of the sling and results in a compressive force. Whenthe leg is extended, the mechanical device tends to withhold the legalong a circular path, while the leg reduces its rotation radius, andtherefore tends to be drawn away from the knee. These compressive andtractive forces, which are proportional to the speed of the movement andto the distance of the knee's sling, are then released on the knee capsand on the articulation's cartilage (compressive force), and on theknee's ligaments (tractive force) respectively.

[0010] The most sophisticated versions of the knee tutors currently usedin sports feature a complex articulated joint which does indeed try tosimulate the compromise between the rotation and sliding movements thattypically occur in the knee. Knee tutors featuring a double centre ofrotation are rather common; however in the positions ranging between 0°and 30° and between 90° and 135° they do not conform to the knee'smechanical physiology. Indeed, in the first arc (0°-30°) no singlecentre of rotation is identified, whereas in the second (90°-135) thesliding movement does not increase to the point of becoming exclusive.Consequently, at these angles, the knee tutor transmits tractive andcompressive forces to the articulation which are released onto theligaments as anomalous tensions.

[0011] On the other hand, in the machines currently used for passivegymnastics, leg curl and leg extension machines.

[0012] These mechanical devices, which are thus bound to the limb, arehinged to an articulated joint which generally has a fixed centre ofrotation and which therefore is unable to provide the combined slidingand rotating movements and change the centre of rotation, therebyproducing anomalous tensions. The latter are caused by the differenttrajectories of the articulated joint's mechanical devices (circle arc)compared to the one theoretically accomplished by the leg (spiral arc).Indeed, as previously described, the leg reduces its radius when itflexes (the above mentioned RB-RA); this causes the mechanical device torub against the leg, bringing about a friction which is passed on to thebelts of the sling and results in a compressive force. When the leg isextended, the mechanical device tends to withhold the leg along acircular path, while the leg reduces its rotation radius, and thereforetends to be drawn away from the knee. These compressive and tractiveforces, which are proportional to the speed of the movement and to thedistance of the knee's sling, are then released on the knee caps and onthe articulation's cartilage (compressive force), and on the knee'sligaments (tractive force) respectively.

[0013] The most sophisticated versions of the knee tutors currently usedin sports feature a complex articulated joint which does indeed try tosimulate the compromise between the rotation and sliding movements thattypically occur in the knee. Knee tutors featuring a double centre ofrotation are rather common; however in the positions ranging between 0°and 30° and between 90° and 135° they do not conform to the knee'smechanical physiology. Indeed, in the first arc (0°-30°) no singlecentre of rotation is identified, whereas in the second (90°-135) thesliding movement does not increase to the point of becoming exclusive.Consequently, at these angles, the knee tutor transmits tractive andcompressive forces to the articulation which are released onto theligaments as anomalous tensions.

[0014] Attempts to solve this problem have been described in theEuropean Patent Application No. 89117781.8 published under No. 0 361405, in the International Patent Application PCT/US92/01929, publishedunder No. WO 92/15264, and in the International Patent ApplicationPCT/US84/00336 published under No. WO 84/03433.

[0015] The knee joint described in the European Patent Application No.89117781.8 is based on the opposite physiological concept whereby theflexing of the knee consists in the fore movement of the femoralcondyles with reference to the tibia condyles, followed by a sheerrotation between the condyles of the aforementioned bones. This jointfeatures three plates, of which the two outer ones feature coaxialholes, while the inner one features two grooves wherein a pair of pinsthat cross through the aforementioned holes in the outer plates arelodged and guided. One of the grooves is small and extendslongitudinally and transversally from the vertical axis of the joints,while the other groove is large and is shaped like a circular segmentwith one end growingwider towards the top. The second slit islongitudinal with reference to the axis of the joints.

[0016] The first groove, the linear one, has the function of reproducingthe first fore movement of the femur with reference to the tibia, whilethe second groove serves the purpose of guiding the subsequent rotationmovement. The upper end of the circular slit is placed on the extensionof the longitudinal axis of the arm of the central plate which passesthrough the centre of the pin lodged in the linear groove, preciselywhen the pin is halfway through the stroke performed by the pin insidethis groove. The centre of the circular segment that constitutes thearched groove consists in the centre of the pin lodged in the lineargroove when the pin itself is at the end of the said groove, which isthe one farthest from the circular groove. When the leg flexes, in thefirst 25° the pin lodged in the circular groove compels the pin in thelinear groove to move from its starting position (closer to the circulargroove) to its final position (at the end of the linear groove that liesfarthest from the circular groove).

[0017] As the distance between the centres of the pins is equal to thebending radius of the circular groove, in this first part of themovement performed by the pin lodged in the linear groove, the pinlodged in the circular groove performs a small vertical Y-shapedmovement within and outside the widened part that constitutes the upperpart of the circular groove. In this first phase of the flexing movementthe two outer plates slide forward with respect to the inner plate(traction or pulling apart phase of the two plates). Subsequently thetwo outer plates rotate onto the inner one as the pin in the end ofstroke position in the linear slit acts as a fulcrum and compels the pinlodged in the circular slit to move. In this second phase the plates aredrawn together again (sheer rolling phase).

[0018] The joint described in the International Patent Application No.PCT/US92/01929 features an improvement of the afore described EuropeanPatent Application No. 89117781.8. As in the previous case, at firstthere is a horizontal translation of the pin lodged in the linear groovefor an angle α1 of approximately 25-35° of the flexing movement, withthe leg outstretched in the starting position. As a result, the tibia ismade to slide back with reference to the femur. In this joint too in thefirst phase of the flexing movement the pin lodged in the circulargroove moves up and down by a Y quantity at the upper end of thecircular groove when the pin lodged in the linear groove passes throughthe latter.

[0019] This first phase of the movement is the followed by a secondphase for an angle α2 which goes as far as 120-135° of the flexingmovement. This second phase is characterised by an essentiallysingle-centred movement: the pin, which at the end of the stroke ispositioned in the linear slit acts as a fulcrum and compels the pinlodged in the circular groove to translate inside the latter.

[0020] Compared to the European Patent Application No. 89117781.8, theimprovement of the present joint consists in the attempt to modify theshape and/or the position of the grooves whenever the conditions of agiven patient should make this advisable.

[0021] The bend of the circular groove which extends beyond 35° of theflexing movement is thus made flatter and the linear groove is extendedslightly towards the distal (i.e. farther) end from the circular groove.In the first phase of the flexing movement (from 0° to 25°, angle α1),the pin lodged in the linear groove moves distally, as a result of whichthe tibia is made to slide behind the femur in this first phase.Subsequently, from 25° to 35° of the flexing movement (angle α2) thelatter pin stays still and thus will constitute the fulcrum around whichthe pin inside the circular groove will rotate.

[0022] Lastly, from 90° to approximately 135° of the flexing movement(angle α3), the pin in the linear groove will be forced to draw closerto the circular one when the other pin moves downwards in the flattenedpart of the circular groove, thereby producing a multi-centred movementin which the tibia moves in front of the femur.

[0023] Even without engaging in a controversy with the inventor of theaforementioned Patents with reference to his conceptual hypothesis onthe physiological movement of the knee, it must be said that althoughhis patents have attempted to tackle these kinds of problems they havenot hit the mark. The basic model of the joint he has invented is basedon the initial movement of the pin lodged in the linear groove in allits length and simultaneously on the upward and downward movement (Y) ofthe other pin. Indeed, in its basic model the joint features twocentres—one that performs a rotation whose median axis runs vertically,and the other whose median axis runs horizontally. The first phase ofthe movement between the plates occurs around the pin lodged in thecircular groove (in this phase, in order to move, the plates aresubjected to a traction and are drawn apart from one another).

[0024] On the other hand, the second phase of the flexing movement(between 25° and 135°), features the rotation of the pin that is lodgedin the circular groove with the other pin as its fulcrum. In this phasethe pin snaps over the pin lodged in the linear groove, around which thejoint develops the second part of its trajectory.

[0025] By applying this mechanical principle inside the knee, one mightsuppose that the latter functions with a series of jerks. This is farfrom true, as the movement that occurs between the articular capsfeatures no gaps at all and is mostly a rotation movement onto which asliding movement progressively prevails.

[0026] Furthermore, at first the circular groove compels the plates towithstand the above mentioned traction (i.e. forces them to be pulledapart from one another) in order to move. The movement performed by theplates is therefore not continuous. The personalisation of the curve foreach individual patient is therefore absolutely uncertain.

[0027] The knee tutor joint described in the International PatentApplication No. PCT/US84/00336 consists in 5 plates. The two outer ones,connected to the supporting elements of the lower leg, each feature ahole and a linear groove. The two intermediate plates also feature ahole and a linear groove each, but in the opposite position compared tothe holes and grooves of the outer plates.

[0028] The central plate, which is connected to the supporting elementsof the upper leg, features a central hole and a bending groove whichextends completely within the plate itself and which simulates thecrosswise course of a flexing point on a given patient's knee.

[0029] The plates are locked onto one another and they can each pivotaround one another and around the central shaft. This shaft extendsthrough the linear grooves in the outer plates and the central holes ofthe intermediate and central plates.

[0030] A pin passes through the (peripheral) holes of the two outerplates, the linear grooves in the intermediate plates and the bendinggroove of the central plate.

[0031] The central shaft and the pin lock the plates onto one another insuch a way that the restricted movement of the pin inside the bendinggroove limits the movements of the supporting elements of the lower legwith respect to those of the upper leg: hence, the flexing and extensionof the patient's lower leg is limited.

[0032] The bending groove lodges some flexible pistons, which act assprings. These can move and are fastened to the ends of the grooves inorder to limit the movement of the pin and, consequently, the width ofthe flexing movement. These flexible pistons are locked by two threadedbolts next to each of which lies an indicator that moves longitudinallyto the pistons themselves. The function of the indicators is to indicatethe degrees of movement allowed in the flexing and extension movements:from 0° to 140°. If one postulates that the central plate stays still,in this joint the intermediate plates rotate and move with respect tothe central one. The outer plates rotate along with the intermediateones but they move to the side of the latter plates along the axis inthe direction of the linear grooves in the intermediate and outerplates. In this system the outer plates move (rotate and slide) withrespect to the central plate.

[0033] The central shaft and the pin that passes through the peripheralholes of the outer plates also change distance in accordance with theangle of the joint in the flexing movement and in accordance with thebending groove, located on the central plate, which simulates thecrosswise course of a flexing point on a given patient's knee.

[0034] However, there is no prior identification of the centre of theknee; this centre ought to be aligned with the central shaft.Furthermore, the possibility of personalising the bending groove is notdescribed other than by referring to the extreme limits imposed on themovements.

[0035] In the machines currently used for passive gymnastics, the hingerotates around a fixed centre and cannot accompany the flex/extensionmovement with a physiological trajectory. Hence, anomalous tractive andcompressive tensions are formed and released onto the ligaments.

[0036] Weight-lifting machines are used to strengthen groups of musclesin a voluntary way. As previously mentioned, the machines currently usedfor the muscles in the knee are the leg curl and leg extension machines.The former selectively strengthens the knee's flexor muscles, while thelatter focuses on the extensor muscles.

[0037] A leg extension machine is very similar to a rather high chair.When seated upon it the feet cannot touch the ground and the thighs arebound to the seat by means of straps or other constraints. A mobile loadarm L (FIG. 6) is located in the centre of the seat (see FIG. 4), orbeside it (see FIG. 5), and runs vertically, along the longitudinal axisof the leg, rotating around a fixed centre C, which constitutes thefulcrum of the entire system. Its rotation axis “c” ought to correspondto the horizontal axis which passes through the femoral condyles (whichis believed to be the centre of the knee).

[0038] An M-shaped horizontal rod is attached to the distal (farther)part of this mobile arm L, and the distal part of the leg exertspressure on this very rod. The leg's extension from the thigh, whichmakes the arm L rotate around axis “c” is withstood by the resistance ofweight P, featured by the machine. This weight P can be connected bymeans of a transmission system (ropes and pulleys) to mobile load arm Litself (as can be seen in FIG. 3), or to a rotation mechanism (FIG. 5).In the latter case, a driving shaft N (with a rotation axis thatcoincides with the aforementioned “c” axis) connects the mobile arm L tothe articulated joint.

[0039] When the lower part of the leg stretches, with the thigh bound tothe machine's seat and the lower part of the leg free to move,mechanical shear and bending stresses are exerted.

[0040] When the flex/extension movement of the lower part of the legoccurs, a number of rebound phenomena take place which are proportionalto the load (weight P) and to the velocity with which the load itself islifted.

[0041] In order to avoid exerting these stresses, especially in patientswho have just undergone surgery in the crossed ligaments, the lower partof the leg should also be bound in several points by some sort of sling(see FIG. 7), so as to make it as integral as possible to mobile loadarm L. The latter, which is hinged to the frame of the weight-liftingmachine, releases rebound phenomena on the central rotation pin, therebysparing the crossed ligaments.

[0042] The major flaw in the machines currently on the market lies inthe fact that the leg sling (FIG. 7) cannot be made to rotate around afixed centre because the knee, as previously stated, has no singlecentre of rotation and therefore cannot, as it moves, run along acircular path, but rather must perform a spiralling movement towards thecentre. Hence, if the limb is fixed to mobile arm L of the machine, itexerts its rotating movement onto the leg, tugging it as it flexes (whenthe leg gradually reduces the radius of its trajectory, and, vice versa,compressing it as it stretches, thereby creating anomalous tensionswhich are released on the crossed ligaments, the knee caps and thearticulatory cartilage.

[0043] The above considerations hold true with reference to an averageknee. However, the length of the crossed ligaments, their proportionsand their point of insertion (features which characterise articularsurfaces), differ considerably from one individual to the next. Thismeans that the spiralling movement made by the knee differs in everyindividual. In order to examine the actual articular profile of a givenknee it is therefore necessary to take X-rays or to measure the distancebetween the knee and the malleolus of the individual.

DISCLOSURE OF INVENTION

[0044] The purpose of this invention is to provide users with anarticulated joint number of rebound phenomena take place which areproportional to the load (weight P) and to the velocity with which theload itself is lifted. In order to avoid exerting these stresses,especially in patients who have just undergone surgery in the crossedligaments, the lower part of the leg should also be bound in severalpoints by some sort of sling (see FIG. 7), so as to make it as integralas possible to mobile load arm L. The latter, which is hinged to theframe of the weight-lifting machine, releases rebound phenomena on thecentral rotation pin, thereby sparing the crossed ligaments.

[0045] The major flaw in the machines currently on the market lies inthe fact that the leg sling (FIG. 7) cannot be made to rotate around afixed centre because the knee, as previously stated, has no singlecentre of rotation and therefore cannot, as it moves, run along acircular path, but rather must perform a spiralling movement towards thecentre. Hence, if the limb is fixed to mobile arm L of the machine, itexerts its rotating movement onto the leg, tugging it as it flexes (whenthe leg gradually reduces the radius of its trajectory, and, vice versa,compressing it as it stretches, thereby creating anomalous tensionswhich are released on the crossed ligaments, the knee caps and thearticulatory cartilage.

[0046] In this specific sector some devices are known to exist that arecapable of reducing the tensile stresses exerted on the leg. The onedescribed in U.S. Pat. No. 5,020,797 is aimed at allowing a leg injuredin the knee to exercise, by applying a resistance force onto the leg.The leg can be extended against this resistance in a given direction, atthe same time it is able to prevent a sub-dislocation in anotherdirection close to the abovementioned knee.

[0047] This device includes a fastening device connected to a mobile armwhich, in turn, is connected to an exercise machine, two shafts, eachwith its own fulcrum, connected to the aforementioned device, a slingconnected to the fastening device to perform a pivoting movement aroundthe first shaft, and another sling that is also connected to thefastening device for pivoting around the second shaft and a levermechanism.

[0048] The latter features an upper arm connected to the first sling, alower arm connected to the second sling, and a lever coupling inproximity to the adjacent ends of the aforementioned arms used to pivot.

[0049] The first sling is connected to a protruding part of the upperarm of the lever. One must first apply a supporting force in onedirection next to one end of the aforementioned first bone, as thisfirst end is close to the aforementioned articulation. The second slingis connected to a protruding part of the lower arm of the lever. This iswhere a second resistance force is to be applied in another directionclose to another end of the aforementioned first bone.

[0050] This device serves the purpose of avoiding a sub-dislocationthrough means that are applied next to the lower part of the leg. It isentirely unrelated to leg tractions having the knee as the fulcrum.

[0051] Indeed, this patent enables the tibia to advance “properly” inthe extension movement which turns out to have been “proper” only whenthe starting position is “improper”, that is to say if the centre of theknee is set back (but not excessively so) with reference to the centreof the machine. Should the centre of the knee be casually placed(indeed, no description of how to identify it is available) andtherefore be aligned to the centre of the machine or advanced, the abovementioned system brings about the advancement of the tibia and exerts astress on the fore crossed ligament. Another device known to exist isdescribed in the French Model No. 83 13474 published under No.2.550.708, which allows the reduction of the pressure in the knee'sjoint when exercising the quadriceps muscles. This device features anarm endowed with weights pivoted onto a joint, a horizontal shaft thatpasses through the joint itself and a resistance arm. Special slingskeep the patient still on a chair so that the joints of one knee arefastened. The usual rod of the resistance arm is replaced by a specialfastening shoe which features fastening strips whereby the patient'sfoot is locked to the shoe itself. The latter is locked onto a staffwhich is connected to the free end of an arm that constitutes a part ofa three-arm lever that can rotate around the shaft.

[0052] One of the three arms consists in an indicator that indicates onan angular scale the traction or rotation movement of the foot. The saidscale is rigidly borne by a sleeve, which can be moved to the resistancearm in an arbitrary position by means of a screw. An elastic componentis mounted on a pin which in turn is rigidly fixed to the said sleeve.

[0053] When the patient is exercising the quadriceps muscle and extendsthe leg, and makes the foot rotate upward the immobilising shoe ispulled upward and toward the left. This exerts a tensile stress on thefoot of the patient. This traction or rotation movement brings about acompression of the elastic component. The width of the compression,which depends on the upward movement of the shoe, is indicated in theangular scale of the abovementioned indicator.

[0054] Hence, a traction occurs in the longitudinal direction of thelower part of the leg. Thus the pressure in the articulation of the kneediminishes and no pain is felt in the knee when taking exercise. Thetraction is brought about automatically when the patient extends the legor moves the lower part of it around the articulation of the knee. Thewidth and the variation of this traction depend both from thecharacteristics of the elastic component and from the distance between,on the one hand, the trajectory of a point that coincides with thefastening elements of the lower part in the patient's leg rotatingaround the articulation of the knee, and, on the other, the trajectoryof a point that coincides with the immobilising shoe rotating around theaxis of the same joint (that is to say, the distance of the position ofthe rotation axis of the resistance arm with reference to the positionof the articulation of the knee).

[0055] By placing the rotation axis of the resistance arm of thistraining device forward and above the articulation of the knee, it ispossible to vary the traction curve in such a way that the maximumtraction is achieved for a preestablished position (angular) in themovement between the position wherein the knee is completely bent (90°)and the one wherein it is completely extended (0°).

[0056] By placing the two axes eccentrically in a given position withreference to one another the traction force can be made to increasegradually with the pressure in the articulation.

[0057] This device constitutes an attempt to solve the problems relatedto moving the knee by using a lever mechanism which is applied to thepatient's foot. It rightly assumes that the alignment between therotation axis of the device's resistance arm and the rotation axis ofthe articulation of the knee is essential, but instead of acting on theknee itself it tries to increase the tensile stress on the articulation.

[0058] This last patent brings about a traction of the leg with respectto the thigh during the flex-extension. This occurs in order tocounterbalance the cohesive stresses caused by the quadriceps musclewhich can contract painfully. The modulation of this tension occurs byplacing the centre of the knee in correspondence with the centre of themachine. Hence a system for the exact identification of the centre ofthe knee is required.

[0059] The problem then consists in accompanying the knee while it moveswithout allowing other mechanical stresses to interfere in its movement.In this case, once again, we have no personalisation of the trajectoryeven though each subject has its own flex-extension trajectory.

[0060] In conclusion to all of the above it can be said that each one ofthe examined patents has made an attempt to find a solution to a givenatypical problem observed in the flex-extension mechanics of the knee.

[0061] None of the inventors has thus addressed the issue by makingconsiderations which could connect all these phenomena and identify acommon denominator. This very common denominator can be found in thedefinition of an efficient methodology for the assessment of thearticulation which must, at first, envisage the identification of ananthropometric point of reference, and subsequently its alignment with ameasuring device. This point must always be found in as much as it isessential not just for a correct assessment but also to align properlyany device to be connected to the knee itself (knee tutor, passivegymnastics machines, weight-lifting machines).

[0062] Furthermore, the definition of an efficient methodology enablesthe correct identification of the trajectory made by the knee in theflex-extension, a trajectory which must surely be accompanied by adrawing of the articular surfaces of the tibia and femur and thesuccession whereby the rotation and sliding movements are combined.

[0063] The above considerations hold true with reference to an averageknee. However, the length of the crossed ligaments, their proportionsand their point of insertion (features which characterise articularsurfaces), differ considerably from one individual to the next. Thismeans that the spiralling movement made by the knee differs in everyindividual. In order to examine the actual articular profile of a givenknee it is therefore necessary to take X-rays or to measure the distancebetween the knee and the malleolus of the individual.

DISCLOSURE OF INVENTION

[0064] The purpose of this invention is to provide users with anarticulated joint endowed with a mobile arm L that is capable of guidingthe flex/extension movements of the leg along a trajectory which mayreproduce as naturally and faithfully as possible the movement that ismade performed by the knee's articular surfaces: sheer rotation,sliding-rotation and sheer sliding. Another aim is that of creating adevice that can easily be modified, so that it may be adapted to theanthropometric characteristics of each subject.

[0065] These and other objectives are indeed achieved by this invention,which consists in an articulated joint with a variable and controllablerotation radius to be installed in weight-lifting machines (legextension and leg curl), on machines for the passive gymnastics of thelower limbs, and on knee tutors (knee guides).

[0066] In its simplest version, this articulated joint consists of twomechanical components, A and B, preferably shaped as round plates. Thesetwo plates A and B can move freely upon one another when neither islocked to a fixed structure. Alternatively, plate A can be fastened to afixed structure by means of a fastener (with plate B rotating uponitself), or plate B can be locked to a fixed structure (in which caseplate A will rotate upon itself).

[0067] When both plates A and B are unlocked the articulated joint maybe used in knee tutors and in passive gymnastics machines, where thethigh and leg move simultaneously; while when either one of the platesis locked the articulated joint is recommended in the leg extension andleg curl machines, where the thigh is bound to the seat of the machineand the flex/extension movement can only be performed by the leg.

[0068] The choice of locking either plate A or B to the machine is madeaccording to the type of transmission used for the resistance (weight P)of the machine, which can be attached either to the mobile load arm ordirectly to the pin of the articulated joint itself. Hence, two casesmay occur: an articulated joint with two plates and with the load onmobile arm L, or an articulated joint with the load on the pin of thejoint itself.

[0069] If the resistance is attached directly onto the mobile load armof the machine, plate A will be locked by means of a fastener, such as abar on the leg extension and leg curl machines. Plate B is then free torotate onto plate A with reference to a horizontal axis “c” which mustcorrespond to the axis of the femoral condyles of the subject whenseated.

[0070] Plate B features two openings at a right angle to the rotationsurfaces of the plates. The first opening is located in the centre anddevelops lengthwise; it is rectangular in shape and the shorter sidesshould preferably be rounded; this opening is made by extending an idealhole and constitutes the axis of symmetry of mobile load arm L featuredby plate B.

[0071] The ends of the second opening, located peripherally, shouldpreferably be rounded. The centre of one of the ends of this secondopening is located on a point located at a distance “I” from the centreof the aforementioned ideal hole, and lying on radius “b”, at a rightangle to radius “a” and on the same plane. The centre of the other endof the second opening is located at 130-140° with reference to radius“b”.

[0072] The second opening had specific shape: initially, for the first15-45° with reference to the aforementiond radius “b”, it is acircumference whose centre coincides with that of an ideal central holeand whose radius is equal to “I”; subsequently, for the remaining85-125°, it is a spiral which returns towards the centre of the idealhole. The sequence of points forming the longitudinal axis of thisspiral is derived from the sequence of points of one end of a section oflength “I”, whose other end moves along the longitudinal axis of thefirst opening.

[0073] Alternatively, the above mentioned peripheral opening can alsoconsist in a groove having a similar shape, with its cavity facing therotation surface of plate A.

[0074] The latter features two pins whose longitudinal axis is at aright angle to the rotation surfaces of plates A and B. These pins arelocated at a distance equal to “I”. The first pin is situated in thecentral part of plate A and is housed in the opening at the centre ofplate B; the second pin is placed in the peripheral opening of plate Bitself.

[0075] The pins are cross-through pins and feature, at the distal (i.e.farther) end, a constraint which prevents the two plates fromseparating. Should the second opening (peripheral) be replaced by agroove, the second pin will not be cross-through and will feature noconstraint on its distal end.

[0076] Actually, the plate endowed with pins can either be the onelocked to the weight-lifting machine (A) or the one that is free torotate on the former (B). Furthermore, it is possible for each plate A,B to be endowed with a single opening and a single pin, provided thatthey alternate: one plate will feature an opening and a pin which willbe lodged in the opening of the other plate. In the articulated jointfeaturing two plates in which the load is attached to the pin of thejoint itself, plate B is fastened to the machine, and the resistance ofthe machine itself (weight P) is transmitted to mobile arm L by means ofa driving shaft, whose longitudinal axis is located on the extension ofaxis “c” of the knee; this shaft acts both as fulcrum for plate A (andfor mobile arm L, which constitutes its extension), and as a propellershaft. Plate A, which constitutes the proximal (i.e. closer) end ofmobile arm L, features the aforementioned central, rectangular openinginstead of the central hole.

[0077] In the case of the articulated joint featuring two plates inwhich the load is attached to the pin of the joint itself, the centralpin constitutes one end of the propeller shaft, which is endowed on theother end with a feather key lodged in the central, rectangular openingof plate A. In order to prevent the pin/shaft from sliding out of plateA, the latter features (in proximity to the feather key) a threaded areaonto which a bolt or other stoppage is screwed. The central openingwhich in this case is on plate A remains unchanged in its engineering,compared to the description made of plate B in the articulated jointwith two plates and with the load on mobile arm L; there is an ideal“central” hole which is the main locating spot. However, the length ofthis opening is increased vertically according to the size of thefeather key, whose point of symmetry (where the transverse andlongitudinal axes meet) must coincide with the ideal hole.

[0078] Plate B is crossed by a hole whose centre must correspond to thecentre of the aforementioned ideal hole, where the central pin/propellershaft is to be lodged and allowed to rotate freely.

[0079] The motion of the shaft does not affect plate B (which isfastened to the machine by means of a fastening bar); rather, the motionis transmitted by means of the feather key inserted in the centralopening of plate A to plate A itself. The latter, in turn, will followthe previously described movement of the second opening on plate B,compelled to do so by the presence of the second pin that is fastened toplate A and lodged in the peripheral opening in plate B.

[0080] Even though suitable for an “ideal” knee, an articulated jointthus made cannot be adjusted to the anthropometric characteristics ofeach individual. Consequently, each knee requires a plate of its own,with a suitable peripheral opening.

[0081] In order to make the articulated joint more versatile, plate B isreplaced by five plates C, D, E, F, G, preferably shaped like a disc, orlike a fraction of a disc, and overlapping.

[0082] In this case too, with a multiple plate articulated joint, plateA can move independently of the group of plates C, D, E, F, G, as is thecase in knee tutors and/or in machines used for passive gymnastics.

[0083] Even when applying the multiple plate articulated joint to legextension and leg curl machines, two versions are possible, according tothe type of transmission of the resistance (weight P) featured by themachine. The following two cases are therefore possible: a multipleplate articulated joint with the load on mobile arm L, or a multipleplate articulated joint with the load on the pin of the joint. In amultiple plate articulated joint used on a weight-lifting machine inwhich the resistance (weight P) is applied directly to the mobile loadarm, plate A is constrained by a fastener, such as a bar on the legextension and leg curl machines; another plate H is in turn fastened toplate A and acts as a cover. The remaining five plates or semi-plates C,D, E, F, G are connected to one another and are free to rotate betweenplates A, H with reference to a horizontal axis “c”, which mustcorrespond to the one crossing the femoral condyles of the subject whenseated. The other four semi-plates D, E, F, G arranged in overlappingcouples are fastened onto plate C, a little farther away from plate A(close to plate H). These four semi-plates D, E, F, G have a particularconformation. Plate F, which is close to plate A, features thepreviously described central, rectangular opening. One of thesemi-plates C, E, F is endowed with a mobile arm. When the twosemi-plates F and G, which are closer to plate A, are side by side theyfeature the previously described peripheral opening, whose radius “d”divides the opening in two parts: one containing the circle arc and theother containing the spiral arc. An ideal point of rotation is locatedon radius “d”, at a distance “I” from the ideal central hole.

[0084] The aforementioned plates D, E, F, G are cut according to axis“e” which goes from this point of rotation to the point of intersectionof radius “f” with the outer edge. Radius “f” is therefore in a positionwhich is diametrically opposite to radius “b”.

[0085] These plates D, E, F, G are arranged in overlapping couples (C,D, and F, E); their overlooking edges have not been cut precisely alongthe axis “e” but rather (considering the aforementioned ideal point ofrotation to be the starting point), they diverge for a few degrees fromaxis “e” in the direction of the mobile arm, or in the oppositedirection. Hence, a distance is created in correspondence with theintersection of axis “e” with radius “f” between the two groups ofsemi-plates (D, G, and E, F); this allows the rotation of one couple ofsemi-plates (D, G) on the other (E, F), with the aforementioned idealpoint of rotation as the rotation fulcrum. By means of a screw, it ispossible to adjust to the micrometer the distance between the two coupleof semi-plates.

[0086] In other words, semi-plate D, which is fastened to semi-plate Conly by means of the pin located in the aforementioned ideal point ofrotation, can rotate with reference to semi-plate E, which ispermanently fastened to plate C. As semi-plate G is fastened tosemi-plate D, and semi-plate F to semi-plate E, semi-plate G can rotatewith reference to semi-plate F. Given that semi-plate G features thespiralling part of the peripheral opening, the latter's position mayvary (owing to the rotation around the above mentioned ideal point ofrotation) with reference to the concentric part of the peripheralopening itself.

[0087] Plate A features two holes, one located in the centre, and theother peripherally at a distance equal to “I” with reference to thecentral hole. In the latter a pin is inserted which is lodged in thecentral opening of semi-plate F; this pin simply acts as a fulcrumaround which plates C, D, E, F, G move. A pin is placed in the secondhole and is lodged in the peripheral opening formed by plates F, G.

[0088] By adjusting the micrometric screw which is connected to platesF, G, it is possible to change the distance between these plates (aswell as the position of the spiral side of the peripheral opening), sothat the rotation of plates F, G on plate A (by means of the pinsfeatured by the latter) may correspond as much as possible to theflex/extension of the leg of the subject in question.

[0089] If the multiple plate articulated joint is used on a machine inwhich the resistance (weight P) is applied directly to the pin of thejoint, the previously described plates C, D, E, F, G maintain the samefunction, even though their position is changed. Plates C, E, F arefastened to the machine by means of a fastener, such as a bar, whileplate A and the first pin can move freely. Plates D, G, being connectedto plate C, are also fastened to the machine, but may rotate partiallyon plates C, E, F, thanks to the pin located on the ideal point ofrotation.

[0090] As described previously for the two plate articulated joint wherethe load is attached to the pin of the join, plate A constitutes theproximal (nearer) part of mobile arm L, and is endowed with theaforementioned central, rectangular opening formerly featured by plateF. Furthermore, there is the previously described central pin/propellershaft, featuring the feather key lodged in the opening of plate A, and athreaded area onto which another plate H is screwed, or a bolt acting asa cover for the entire system.

[0091] Plates C, E, F are crossed by a hole whose centre must correspondto the centre of the previously mentioned ideal hole in which thecentral pin/propeller shaft will be lodged and allowed to move freely.

[0092] The motion of the propeller shaft does not affect plates C, E, F,which are fastened to the machine by means of a fastening bar; rather,the motion is transmitted by means of the feather key inserted in thecentral opening of plate A to plate A itself. The latter, in turn, willfollow the previously described movement of the peripheral opening onplates F, G, compelled to do so by the presence of the second pin thatis fastened to plate A and lodged in the peripheral hole.

[0093] Irrespective of the number of plates and of the fastening systemused to bind them to the machine in the proximal part of the mobile arm,an opening is made in which a mechanical hook is inserted allowing it torun along the opening itself. On this mechanical system the sling to beused for the shins will be fastened, approximately below the knee.

[0094] Furthermore, the mobile arm features another opening, locateddistally, wherein a feather key is lodged which is allowed to run freelybetween axis “a” of the mobile arm itself. The foot rest is attachedonto this feather key; a pin can lock the feather key to the mobile arm.

[0095] The above mentioned foot rest consists in a blade or plate whichis bent on one end at 90°, or by two joined blades or plates united at90°. The vertical part of the rest is joint to the mobile arm, while thehorizontal part is the place where the foot actually rests, locked inposition by means of a small belt.

[0096] In the weight-lifting machines where the load is applied on thepin of the articulated joint, irrespective of whether a two plate or amultiple plate system is used, the articulated joint can be modifiedwhen the central pin/propeller shaft is wider than plate A.

[0097] In this case, a guide is milled on the central pin/propellershaft, wherein plate A is placed; the latter's ideal central holecorresponds to the centre of the central pin/propeller shaft, the latterfeaturing a threaded hole.

[0098] A three-part screw featuring head, body and thread, and whosethreaded part is engaged in the threaded hole of the centralpin/propeller shaft, keeps plate A within the guide, with itsnon-threaded section going beyond the central opening. The head of thescrew prevents the separation of the two mechanical parts.

[0099] When the leg transmits the motion to arm L, which is fastened toplate A, the proximal part of plate A, which is inserted in the guide ofthe central pin/propeller shaft, transmits this motion to the centralpin/propeller shaft itself through the contact of the sides of plate Awith the internal surfaces of the central pin/propeller shaft guide.

[0100] The second pin featured by plate A, which is lodged in theperipheral opening of plate B, makes plate A and arm L, which isconnected to it, go along a trajectory with a varying radius, parallelto the one of the leg in the sling of arm L.

[0101] This variation in the radius during the flex/extension trajectoryof the leg from the thigh makes plate A within the guide translate; thescrew/pin, which in turn is inserted in the central opening, does nothamper this translation.

[0102] In using a multiple plate articulated joint on weight-liftingmachines, a degree angular scale is to be drawn in an appropriate spoton a plate. The 0 position will correspond to the longitudinal axis ofthe mobile arm when the latter is the extension of the bar which joinsthe device to the machine. The scale develops in the opposite directionin which the peripheral opening is developed.

[0103] Parallel to the distal opening in the mobile arm, on the outeredge or on the side opposite that to which the leg is fastened, averification linear millimeter scale is located, whose ideal zero is theideal central hole.

[0104] Instead of degree scales, two encoders may also be used tomeasure the movements simultaneously, ore located in the place of thelinear scale, the other in the place of the angular scale.

[0105] The above mentioned pins inserted in the central and peripheralopenings can be ellipsoidal, in order to ease their longitudinal motionwithin the aforementioned openings; they may also be provided withrolling bearings. The number of mobile plates which replace plate B canbe even greater, in order to divide the spiralling part of theperipheral opening into several areas, each one featuring its own centreof rotation. Hence, it is possible to adjust even more precisely theposition of the aforementioned spiral opening.

[0106] Plates C, E, F can consist in a single piece.

[0107] The device which is the object of this patent application can beused on the machines that exist at present and on future machines byremoving the traditional rotation device.

[0108] It can also be used as an accessory in combination with thetraditional mechanism, thereby making the machine more functional.Lastly, the device may also be used as an accessory on other types ofmachines (or seats), thereby endowing them with the same function as legextension and leg curl machines. In the latter case, the fastening barwill be locked onto the machine (or onto the seat) by means of thosecomponents that are known to achieve this aim.

[0109] The use of this invention on weight-lifting machines permits thestrengthening or re-education of the extensor and/or flexor muscles ofthe leg with reference to the thigh, so that the anomalous physiologicalstresses (shear, flex, rebound, tensile and compressive), which occurduring motion may be prevented from releasing harmful tensions on theligaments. Its use in knee tutors (knee guides) similarly avoids thatthe same types of anomalous physiological stresses be released on theknee's ligaments, on the knee-covers, on the articular cartilage ofpeople who have suffered an injury in their knees, or athletes, as theywalk, do sports or perform rehabilitation exercises.

[0110] Indeed, this articulated joint is made in order to permit itscomponent parts to make movements which reproduce as faithfully aspossible the sequence that occurs in the variation of the knee's centreof rotation and the progression of the rotation and sliding movements.Hence, the leg and arm L which is connected to the leg remain ontrajectories that coincide perfectly, so that in each phase of theflex/extensor movement there is a perfect correspondence between everypoint of contact between the leg and arm L. This prevents any kind ofslipping between the mechanical device and the limb, thereby avoidingthe aforementioned anomalous tensions.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Other characteristics and advantages of the invention will bemore evident with the description of some specific and preferred but notexclusive configurations of the articulated joint, indicativelyillustrated in the enclosed drawings in which:

[0112]FIG. 1 illustrates the position of the muscles of the thigh andthe flexing and extension movements;

[0113]FIG. 2 shows the articular surfaces of the knee;

[0114]FIG. 3 illustrates the variation in the distance between thefemoral condyle and the malleolus which occurs during the extension ofthe leg;

[0115]FIG. 4 shows the type of weight-lifting machine that exists atpresent, called leg extension machine, where the weight is placed on themobile arm;

[0116]FIG. 5 shows a leg extension machine where the weight is placed onthe articulated joint;

[0117]FIG. 6 illustrates the movement of the mobile arm on a legextension in knee tutors (knee guides) similarly avoids that the sametypes of anomalous physiological stresses be released on the knee'sligaments, on the knee-covers, on the articular cartilage of people whohave suffered an injury in their knees, or athletes, as they walk, dosports or perform rehabilitation exercises.

[0118] Indeed, this articulated joint provides a solution for theproblems featured by the inventions described in the above mentionedpatents. Its innovative characteristics, which consist in the positionof the central opening that starts at the centre of the plate on thesame axis with reference to the lower point of the peripheral opening,and proceeds along the symmetrical axis of the load arm, a constantdistance I between the pins, and thus a constant distance between thetwo openings when the pins are in motion, and the rotation aound an axis(c) that passes through the femoral condyles of the subject of theplates or semi-plates allow this joint to reproduce as faithfully aspossible the sequence that occurs in the variation of the knee's centreof rotation and the progression of the rotation and sliding movements.Hence, the leg and arm L which is connected to the leg remain ontrajectories that coincide perfectly, so that in each phase of theflex/extensor movement there is a perfect correspondence between everypoint of contact between the leg and arm L. This prevents any kind ofslipping between the mechanical device and the limb, thereby avoidingthe aforementioned anomalous tensions.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Other characteristics and advantages of the invention will bemore evident with the description of some specific and preferred but notexclusive configurations of the articulated joint, indicativelyillustrated in the enclosed drawings in which:

[0120]FIG. 1 illustrates the position of the muscles of the thigh andthe flexing and extension movements;

[0121]FIG. 2 shows the articular surfaces of the knee;

[0122]FIG. 3 illustrates the variation in the distance between thefemoral condyle and the malleolus which occurs during the extension ofthe leg;

[0123]FIG. 4 shows the type of weight-lifting machine that exists atpresent, called leg extension machine, where the weight is placed on themobile arm;

[0124]FIG. 5 shows a leg extension machine where the weight is placed onthe articulated joint;

[0125]FIG. 6 illustrates the movement of the mobile arm on a legextension machine;

[0126]FIG. 7 shows the constraints placed on the slinged leg in a legextension machine;

[0127]FIG. 8 illustrates a prospective view of the articulated jointobject of this patent application featuring only two plates;

[0128]FIG. 9 shows the frontal view of the first of these plates in thisarticulated joint;

[0129]FIG. 10 illustrates a lateral view of the same plate;

[0130]FIG. 11 shows the frontal view of the second of these plates inthis articulated joint;

[0131]FIG. 12 illustrates a lateral view of the second plate;

[0132]FIG. 13 shows an exploded view of the articulated joint withmultiple plates;

[0133]FIG. 14 illustrates a frontal view of the articulated joint andthe mobile arm;

[0134]FIG. 15 shows a lateral view of the same articulated joint and itsrespective mobile arm;

[0135]FIG. 16 illustrates the lateral view of the articulated joint andmakes its structuring theory explicit;

[0136]FIG. 17 illustrates a prospective view of the part of thearticulated joint which is connected to the weight-lifting machine;

[0137]FIG. 18 illustrates the first plate of the mobile part of thearticulated joint;

[0138]FIG. 19 shows the first semi-plate of the mobile part of thearticulated joint;

[0139]FIG. 20 illustrates the second semi-plate of the mobile part ofthe articulated joint;

[0140]FIG. 21 shows the third semi-plate of the mobile part of thearticulated joint which overlaps the one shown in FIG. 19;

[0141]FIG. 22 shows the fourth semi-plate of the mobile part of thearticulated joint which overlaps the one shown in FIG. 20;

[0142]FIGS. 23, 24 and 25 show three different arrangements of theplates of the articulated joint, when the leg is in the extended, flexedat 90°, and flexed at 135° positions;

[0143]FIG. 26 shows the articulated joint applied to a leg extensionmachine where the weight is placed on the mobile arm;

[0144]FIG. 27 shows the articulated joint applied to a leg extensionmachine where the weight is placed on the pin of the articulated joint;

[0145]FIG. 28 shows an exploded view of the articulated jointillustrated in FIG. 27;

[0146]FIG. 29 illustrates a view of a knee tutor featuring thearticulated joint which is the object of this patent application;

MODE FOR CARRYING OUT THE INVENTION

[0147] More precisely, in a first, simplified configuration applied to aleg extension weight-lifting machine with a resistance (P) constrainedto mobile arm L, the articulated joint is formed by two plates 1 and 2;plate 1 is fastened to the weight-lifting machine by means of a bar 1.1,while plate 2 is able to rotate onto plate 1 with reference to ahorizontal axis which passes through the femoral condyles of the subjectwhen seated. An arm 2.1, featuring a horizontal rod located at thefarther end and connected to the weights, is fastened to plate 2.

[0148] Plate 2 features two openings 2.2 and 2.3 at a right angle to therotation surfaces of the two plates. The first opening 2.2 isrectangular in shape and the shorter sides are rounded; this opening ismade by extending an ideal hole 2.4, which is located at the centre ofplate 2, towards the outside along a radius defined as “a” whichconstitutes the longitudinal axis of symmetry of mobile arm 2.1.

[0149] The ends of the second opening 2.3 are shaped like a circle. Thecentre of one of the ends of this second opening 2.3 is situated on apoint located at a distance “I” from the centre of the aforementionedhole 2.4, and lying on radius “b”, at a right angle to radius “a”, whichpasses through the centre of the aforementioned hole 2.4 and on the sameplane. The centre of the other end is located at 135° with reference tothe above mentioned right angled radius “b”. The second opening 2.3 hasspecific shape: initially, for the first 20° (angle α) with reference tothe aforementioned right angled radius “b”, it is a circumference whosecentre coincides with that of the centre of ideal hole 2.4 and whoseradius is equal to “I”; subsequently, for the remaining 115° (angle β),it is a spiral which returns towards the centre of ideal hole 2.4. Thesequence of points forming the longitudinal axis of this spiral isderived from the sequence of points of one end of a section of length“I”, whose other end moves along the longitudinal axis of the firstopening 2.2 (from ideal hole 2.4 radially towards the outside alongradius “a”). Plate 1 features two pins 1.2 and 1.3, whose longitudinalaxis is at a right angle to the rotation surfaces of plates 1 and 2.These pins are located at a distance equal to “I”. Pins 1.2 and 1.3 arecross-through pins and feature distally stop plates 1.4 and 1.5 whichprevent plates 1 and 2 from separating.

[0150] The subject sits with the flexed leg on a leg extensionweight-lifting machine built like the machines currently on the market.The thighs are fastened to the seat by belts or other constraints. Thesubject begins to extend the lower part of the leg, thereby compellingmobile load arm 2.1 to rise. This compels plate 2 to move. Theparticular shape of openings 2.2 and 2.3 gives rise to differentmovements depending on the position of mobile load arm 2.1. Indeed, inthe first phase of the extension (the first 115°: angle β), sinceopening 2.3 is shaped like a spiral that returns towards the centre ofplate 2, and the distance between pins 1.2 and 1.3 is still “I”, plate 2will be compelled to endure a twofold movement: rotation and slidingupwards. As mobile load arm (2.1) is fastened to plate 2, it follows themovements of plate 2, and therefore translates upwards and rotates atthe same time. This movement follows perfectly the movement of the legfastened to mobile arm 2.1 as the latter makes a spiralling trajectory,like the physiological one of the knee. At each point of the extension,each point of contact between the leg and mobile arm 2.1 correspondsperfectly, thereby avoiding anomalous tensions in the knee.

[0151] Subsequently (for the remaining 15-20° of the extension: angleα), as opening 2.3 is a circumference whose centre coincides with thecentre of pin 1.2 or that of hole 2.4, plate 2 will simply rotate ontoplate 1.

[0152] In the return movement the same motions occur but reversed: whenthe leg flexes there is at first a rotation of plate 2 on plate 1,succeeded by a rotation with a translation towards the bottom and,lastly, only a translation towards the bottom.

[0153] For the articulated joint to be personalised, and thus suitablefor each subject, without having to make changes in plate 2, it isnecessary to use a multiple plate articulated joint.

[0154] Indeed, in a second configuration applied to a leg extensionweight-lifting machine with a resistance (P) constrained to mobile armL, plate 2 is replace by five plates 3, 4, 5, 6, 7, shaped like a discor like a fraction of a disc and overlapping. These plates orsemi-plates are connected to one another and are free to rotate ontoplate 1 and onto the last plate 8 (which acts like a cover), withreference to a horizontal axis “c”, which passes through the femoralcondyles of the subject when seated.

[0155] Semi-plates 4, 5, 6, 7, in overlapping couples, are fastened toplate 3, which is the farthest from plate 1 of all. Plate 3 features athreaded hole 3.1 in correspondence with the point of rotation ofsemi-plate 4, onto which a pin 4.1 is screwed, allowing the rotation ofsemi-plate 4 with reference to semi-plate 3. Furthermore, two threadedholes 3.2 are made on plate 3 towards semi-arm 3.3, which locksemi-plate 5 and semi-plate 6 onto plate 3 by means of adequate screws.

[0156] Semi-plates 4, 5, 6, 7 are shaped in a particular manner. Anexamination of the latter two reveals that semi-plate 6 features anopening 9 which is similar to the aforementioned opening 2.2. Thisopening 9 is also obtained by extending an ideal hole 9.1, which islocated at the centre of the semi disc that forms semi-plate 6, towardsthe outside, along a radius defined as “a”, which constitutes thelongitudinal axis of symmetry of the mobile arm 6.1 featured bysemi-plate 6. This mobile arm 6.1 is connected to the weights. When thetwo semi-plates 6 and 7 are side by side they feature a second opening10, similar to the previously described opening 2.3.

[0157] In opening 10 considerable importance is played by radius “d”,which divides opening 10 into two parts: one, 10.1, containing thecircle arc of semi-plate 6 and the other, 10.2, containing the spiral ofsemi-plate 7. Radius “d” is inclined by 20° (on the same plate) withreference to radius “b”. A point 11 is located on radius “d” at adistance “I” from the ideal hole 7.1.

[0158] Semi-plates 4, 5, 6, 7 are cut according to an axis “e” whichgoes from point 11 to the point of intersection of radius “f” with theouter edge (of semi-plates 4, 5, 6, 7); radius “f” is in a positionwhich is diametrically opposite to radius “b”.

[0159] Getting back to the details of the various components, it willappear that semi-plate 5 is fastened, as previously described, in theproximal part of semi-arm 3.3 of plate 3. It features two holes 5.1where as many screws, having the same interaxis as holes 3.2, passthrough. The side which faces semi-plate 4 features indentation 5.2which is slightly shorter than half the circumference and whose centreis in point 11.

[0160] Semi-plate 4 is fastened onto plate 3, next to semi-plate 5. Fromthe side overlooking semi-plate 5 a half circumference 4.2 (whose centreis in point 11) protrudes, whose diameter is lesser than indentation 5.2of semi-plate 5, so as to allow it to be inserted in the latter and thuspermit the rotation between the mechanical members around point 11. Pin4.1 is inserted inside hole 4.3, located at the centre of the halfcircumference 4.2 (endowed with a countersink on the side overlookingsemi-plate 7) placed in correspondence with point 11, around whichsemi-plate 4 rotates. This rotating pin 4.1 is screwed into hole 3.1 ofplate 3. It consists in three parts: head (which is inserted inindentation 4.4 of the half circumference 4.2), body (which is smoothand occupies hole 4.3) and thread (which is to be engaged in hole 3.1).

[0161] Semi-plate 4 also features a threaded hole 4.5, located in thecentre, where a screw fastening semi-plate 7 to semi-plate 4 itself canbe inserted. Semi-plate 6 is fastened to semi-plate 5 and to plate 3 bymeans of screws that cross holes 6.2, 5.1 and 3.2. At the centre ofsemi-plate 6 opening 9 opens up, while in the farther end (distal) frommobile arm 6.1 in the direction of point 11, part 10.1 of opening 10opens up; the latter originates from radius “b” at a distance “I” fromhole 9.1, and develops with a constant radius along a circle arc untilit intersects with radius “d”.

[0162] Pin 1.2 is inserted in opening 9; the former can be locked incorrespondence with ideal hole 9.1. In the channel formed by opening 9spring 12 is inserted; the latter is withheld by a distal spring-lock 13(which is crossed lengthwise by hole) and by proximal spring-lock 14.The latter acts on a bushing 15, within which pin 1.2 is lodged. Thelatter's internal diameter corresponds to the outer diameter of pin 1.2and the outer diameter to the size of opening 9. The mechanicalfinishing of bushing 15 must enable it to rotate freely on pin 1.2, andto slide freely into opening 9. Proximal spring-lock 14 can be pushed bya peg 16, which is lodged in mobile arm 6.1 within an indentation 17that features two locked positions: when one end of peg 16 is insertedin the proximal locked position 17.1 bushing 15, pushed from the otherend by peg 16 itself (after crossing distal spring-lock 13), iscompelled to place itself on ideal hole 9.1; on the other hand, when peg16 is inserted in the distal locked position 17.2 bushing 15 is free tomove within opening 9. Semi-plate 7 is fastened onto semi-plate 4 bymeans of a screw which crosses a countersunk hole 7.1 which is to beengaged in hole 4.5.

[0163] Section 10.2 of opening 10 is carved onto semi-plate 7; theformer extends from radius “d” until the complete development of opening10 itself.

[0164] Semi-plates 5 and 6 feature an edge overlooking semi-plates 4 and7 which is not, however, cut exactly along axis “e” but rather,considering point 11 to be the starting point of the edge, diverges by afew degrees from axis “e” in the direction of mobile arm 6.1.Semi-plates 4 and 7 also feature an edge overlooking semi-plates 5 and 6which is not cut exactly along axis “e” but, unlike the latter plates,and, again, considering point 11 to be the starting point of the edge,rather diverges by a few degrees from axis “e” in the opposite directionfrom mobile arm 6.1.

[0165] As the edge of semi-plates 4 and 7 and that of semi-plates 5 and6 share the same centre but have sides that open in the oppositedirection, a distance is formed where axis “e” intersects with theexternal edge which permits semi-plates 4 and 7 to rotate on semi-plates5 and 6; point 11 is the centre of this rotation movement.

[0166] A wing 6.3 and 7.2 is fastened onto semi-plates 6 and 7, inproximity to the outer edge. A threaded, cross-through hole 6.4 isfeatured by wing 6.3, while wing 7.2 features a non threadedcross-through hole (with the same interaxis). A screw 18 is insertedthrough the latter hole; screw 18 is endowed with a bolt 18.1 which isto be engaged in hole 6.4. By acting on this screw 18 it is thereforepossible to adjust the distance between plates 6 and 7 (and,consequently, also between plates 4 and 5); it is possible to adjustthis distance to the micrometer.

[0167] A pin 1.3, which crosses threaded hole 1.4 (which is on plate 1)is inserted in opening 10. It is made of three sectors: a handwheel witha knurled edge, which makes it easier to lock it manually on plate 1, athreaded sector which is screwed inside hole 1.4, and a non threadedcylinder section which slides inside opening 10 and protrudes from theside opposite the one featuring the handwheel.

[0168] Furthermore, plate 1 also features a second hole 1.5, locatedcentrally, with a longitudinal axis at a right angle to the rotationsurfaces of plates 1, 3, 4, 5, 6, 7, and located at a distance equal to“I” with reference to hole 1.4, within which pin 1.2 is inserted. Thelatter is cross-through and its distal end is lodged inside bushing 15,thereby crossing opening 9. Pin 1.2 also consists in three parts: ahandwheel with a knurled edge, a threaded sector which is screwed insidehole 1.5, and a non threaded cylinder section which slides insideopening 9.

[0169] In the section closer to mobile arm 6.1 lies an opening 19 whichis rectangular in shape (and which follows the direction of axis “a”),inside which a mechanical system 20 with screws is inserted, allowingthis system to move longitudinally along opening 19.

[0170] A small, semi rigid belt 21 is fastened onto mechanical system 20to be tied around the distal part of the belt, approximately below theknee; the possibility to move mechanical system 20 makes it possible toidentify the exact point in which this constraint is to be fastenedaccording to the anthropometric dimensions of the user of the invention.

[0171] Mobile arm 6.1 also features another opening 22, locateddistally, which is also rectangular in shape (possibly with roundedsides) which follows the direction of axis “a”.

[0172] A feather key 23 is lodged inside opening 22; the former isexternally wider than opening 22 and it is thicker than mobile arm 6.1;however, it is allowed to slide freely along axis “a” of mobile arm 6.1.The foot rest is fastened to feather key 23 by means of screws; a pin 24fastens feather key 23 to mobile arm 6.1.

[0173] The aforementioned foot rest consists in two blades 25 fastenedto one another at 90°. The vertical blade allows the connection tomobile arm 6.1 by means of screws which engage in feather key 23; thehorizontal blade allows the foot to rest by coming into contact with alarge portion of the bottom of the foot.

[0174] The foot resting in this location is fastened to blade 25 bymeans of a small belt 26, so as to maintain the position it is in at thestart throughout the flex/extension movement.

[0175] A degree angular scale 1.6 is drawn at the periphery of plate 1.The 0 position is located in correspondence with radius “a” in theposition in which mobile arm 6.1 constitutes the extension of bar 1.1;the scale develops in the opposite direction compared to the directionin which pin 1.3 is located. A verification linear millimeter scale islocated parallel to opening 22. A 0 reference point is drawn on theouter edge of feather key 23.

[0176] The 0 of this millimeter scale 27 is located on ideal hole 9.1and, consequently, the scale only shows values that are higher than acertain level, for instance 30 centimeters. The distance between thecentre of ideal hole 9.1 and the fiducial mark of the millimeter scale27 is called radius “R”. The above mentioned plate 8 acts as a cover; itis connected to plate 1 by means of three screws 28; these screws 28 areinserted inside specific spacing bar 29 which prevent plates 1 and 8from getting excessively close to one another. These two plates aretightly fastened to semi-plates 3, 4, 5, 6, 7, (by means of screws 28),preventing them from being drawn apart from plate 1. Semi-plates 3, 4,5, 6, 7 are allowed to slide onto plates 1, 8 thanks to the use ofself-lubricating substances for contacting surfaces.

[0177] As previously described, the length of the knee's crossedligaments and their point of insertion are individual anthropometriccharacteristics which shape the knee's articular surfaces and whichtherefore differ from one individual to the next. In order to analysethese characteristics and to personalise the articulated joint afunctional assessment is the common approach.

[0178] In order to carry out a correct assessment it is first of allindispensable for the knee to be placed on the machine in a preciseposition; that is to say, the axis which crosses the knee, around whichthe first 15-20° of the flex/extension take place (axis “c”) correspondperfectly to axis “c” of the device, which crosses the centre of idealhole 9.1.

[0179] This alignment of the centre of both the knee and the machine,called self-centring, must be performed before any other step and mustbe performed again every time that the same subject places him/herselfon the machine and need to return to the same working conditions.

[0180] The subject is made to sit down with his leg on the leg extensionmachine. The thigh belts and belts 21, 26 on the distal part of the legare fastened. Mechanical system 20 and pin 24 are released, so that theformer may be free to slide into opening 19 and feather key 23 intoopening 22. After having removed pin 1.3 from plate 1 and having lockedpin 1.2 in the central position (by means of peg 16 which is located inthe proximal locked position 17.1 which locks bushing 15 onto ideal hole9.1), mobile arm 6.1 is used as an arm rotating around a fixed centre(whose centre is ideal hole 9.1 and which is coaxial to axis “c” of thedevice).

[0181] The subject, with the leg outstretched, performs some smallflex/extension movements of approximately 30°, readable in the degreeangular scale 1.6. If when the subject is seated with his limboutstretched the measure of radius R differs from the measure taken whenthe limb is slightly flexed, the knee is not centred and the latter'saxis “c” will not coincide with the axis “c” of the device. Forinstance, if the measure of radius R increases, the knee will be in aforward position with reference to axis “c” crossing the centre of idealhole 9.1. If the measure decreases, the knee will be behind or belowaxis “c”.

[0182] Once the perfect correspondence between axis “c” of the knee andthat of the device has been found, it is possible to trace the articularroute of the tibia as it rolls and slides onto the femur Starting froman outstretched position a few readings are taken, particularly in thelast 90° of the movement, i.e. as the leg flexes between 45 and 135°.

[0183] The measurements to be taken are the flexing angle (to be read ondegree scale 1.6) and the corresponding variation of radius R (to beread on linear millimeter scale 27).

[0184] Having taken a number of such coupled readings, it is possible tocompute mathematically the curve interpolating the points read at themaximum flexing and thus identify the opening 10.2 which best suits thesubject being examined.

[0185] The subsequent personalisation of curve 10.2 is performed onmillimetric screw 18 which is hinged to wings 6.3 and 7.2 of semi-plates6 and 7. By adjusting this screw 18, the distance between plates 6, 7,(and 4, 5) can be adjusted, as a consequence of which the position ofopening 10.2 with reference to opening 10.1 will also be adjusted. Pin4.1 is the fulcrum of the rotation of opening 10.2.

[0186] When opening 10.2 has been adjusted to suit the characteristicsof the subject being examined, peg 16 is placed in the distal lockedposition 17.2, thereby releasing bushing 15. Pin 1.3 is then screwedinto hole 1.4 of plate 1, feather key 23 is locked (by means of pin 24)into opening 22 in correspondence with the reference spot of the foot,and mechanical system 20 is locked in opening 19, thereby definitivelyfastening the distal part of the leg to mobile arm 6.1.

[0187] At this stage, having personalised opening 10.2, the subject maystart performing normal flex/extension exercises. The movements of themultiple plate articulated joint will be similar to those of the twoplate articulated joint. The subject starts from a flexed position toperform and extension of the leg from the thigh, thereby compellingmobile load arm 6.1 to rise.

[0188] This compels plates 3, 4, 5, 6, 7 to move. The particular shapeof openings 9 and 10 gives rise to different movements depending on theposition of mobile load arm 6.1. Indeed, in the first phase of theextension (the first 115°: angle β), since opening 10.2 is shaped like aspiral that returns towards the centre of plate 6, and the distancebetween the two pins is still “I”, plates 3, 4, 5, 6, 7 will becompelled to translate upwards and, at the same time, rotate onto plates1,8. Arm 6.1, which is fastened to semi-plate 6, logically follows thesemovements.

[0189] Subsequently (for the remaining 15-20° of the extension: angleα), as opening 10.1 is a circumference whose centre coincides with thecentre of hole 9.1, plates 3, 4, 5, 6, 7 will simply rotate onto plate1, 8, the fulcrum being ideal hole 9.1.

[0190] On the other hand, the following description concerns aconfiguration of an articulated joint with multiple plates and theresistance of the machine on the rotating device.

[0191] In this case, central pin 1.2 constitutes the end of a shafthaving a longitudinal axis placed on the extension of the knee's axis“c”. Plates 3, 4, 5, 6, and 7 maintain the same function (compared tothe previous multiple plate configuration), even though their positionis changed. Plates 3, 5, 6 are fastened to the machine; plates 4, 7,being fastened to plate 3 by means of pin 4.1 and by the screw crossingholes 4.5 and 7.1, also remain fastened to the machine, but may rotatepartially onto plates 3, 5, 6, thanks to the aforementioned pin 4.1located on the ideal point of rotation.

[0192] Plate 1 constitutes the proximal part of mobile arm 1.1 whichreplaces the mobile arm 6.1 of the previous multiple plate version; itfeatures central, rectangular opening 9, formerly featured by plate 6.Plate 1/arm 1.1 is free to rotate onto plates 3, 4, 5, 6 and 7.

[0193] As previously described, central pin 1.2 here constitutes one endof the propeller shaft, which features on the other end a feather key 30which is lodged in the central, rectangular opening 9 of plate 1. Inorder to prevent pin 1.2/shaft from slipping out of plates 3, 4, 5, 6,7, the latter is endowed with a threaded area, in proximity to featherkey 30, onto which plate 8 is screwed, thereby acting as a cover for theentire system.

[0194] Central opening 9 remains unchanged in its engineering, comparedto the description made in the first case for plate 6, with the idealhole 9.1 as the main locating spot. However, the length of this openingis increased vertically according to the size of feather key 30, whosepoint of symmetry (where the transverse and longitudinal axes meet) mustcoincide with the ideal hole.

[0195] Plates 3, 5, 6 are crossed by a cross-through hole 31 whosecentre corresponds to the centre of ideal hole 9.1, where the centralpin 1.2/propeller shaft is be lodged and allowed to rotate freely.

[0196] The motion of the pin 1.2/propeller shaft does not affect plate3, 5, 6, which are fastened to the machine; rather, it transmits thismotion to plate 1 by means of feather key 30 which is located in opening9. The latter, in turn, will follow the motion suggested by the secondopening on plates 6,7, compelled to do so by the presence of the secondpin 1.3 that is fastened to plate 1 and lodged in peripheral opening 10.

[0197] The invention thus made is subject to several modifications andvariations, all of which pertain to the inventive concept. Furthermore,all details may be replaced with other technically equivalent ones.

1 - Adjustable rotation radius articulated joint for gym machines andknee tutors formed by two or more overlapping mechanical members such asrounded plates (1, 2) placed side by side; at least one plate (1, 2)features a central opening (2.2, 9) which is at a right angle to therotation surfaces of the plates, developed lengthwise and rectangular inshape, preferably with rounded small sides; one plate (2) or more (6, 7)feature a second opening (2.3, 10) located peripherally, which for thefirst 15-45° is a circumference; one or more plates (1) feature two pins(1.2, 1.3) at right angles to the surface rotations of the plates; thefirst pin (1.2) is located in the central position and is inserted inthe aforementioned central opening (2.2, 9); the second pin (1.3) islocated peripherally and is placed in the peripheral opening (2.3, 10);this joint is characterised by the fact that it is formed by more thanone mechanical members, preferably shaped like overlapping roundedsemi-plates (4, 5, 6, 7) arranged in couples (4, 7 and 5, 6) and sidedby circular plates (1, 3, 8); at least one plate (2) or semi-plate (6)features a mobile arm (2.1, 6.1), and at least another plate (1)features an arm (1.1) which can either be mobile or be fixed to theweight-lifting machine; the aforementioned central opening (2.2, 9) islocated on a plate (2) or semi-plate (6) and has been made starting froman ideal hole (2.4, 9.1) located in the centre of the plate (2) orsemi-plate (6) and then proceeding towards the mobile arm (2.1, 6.1)along a radius (a) that constitutes the axis of symmetry of the mobilearm itself (2.1, 6.1); the aforementioned peripheral opening (2.3, 10)is located on a plate (2) or two overlapping semi-plates (6, 7); one endof this peripheral opening (2.3, 10) is located at a distance “I” fromthe centre of the above mentioned central ideal hole (2.4, 9.1), whichlies on a radius (b), at a right angle to radius (a) and on the sameplane, while the other end is located at 135° with reference to thisright angled radius (b); this peripheral opening (2.3, 10) has specificshape: initially, for the first 15-45° with reference to theaforementioned right angled radius (b), it is a circumference whosecentre coincides with that of the centre of the above mentioned idealcentral hole (2.4, 9.1) and whose radius is equal to I; subsequently,for the remaining 90-120°, it is a spiral which returns towards thecentre of the ideal hole (2.4, 9.1); the sequence of points forming thelongitudinal axis of this spiral is derived from the sequence of pointsof one end of a section of length “I”, whose other end moves along thelongitudinal axis of the first opening (2.2, 9) towards the mobile arm(2.1, 6.1); inside the said peripheral opening (2.3, 10) a radius (d)divides the opening (2.3, 10) in two parts: one (10.1) containing thecircle arc and the other (10.2) containing the spiral arc; if twooverlapping semi-plates are being used (6, 7) one semi-plate (6) willfeature the circular part (10.1) of the opening (2.3, 10), while theother semi-plate (7) will feature the spiralling part (10.2) of theperipheral opening itself (2.3, 10); an ideal point of rotation (11) islocated on radius (d) at a distance “I” from the ideal central hole(2.4, 9.1); the aforementioned pins (1.2 and 1.3) are located at adistance equal to “I” and the first pin (1.2) can also consist in oneend of the propeller shaft; the plates or semi-plates rotate around anaxis (c) which passes through the subject's femoral condyles; theseplates or semi-plates can move freely onto one another when no plate isfastened to a fixed structure, as is the case with knee tutors andpassive gymnastics machines; alternatively, a plate (1) can be fastenedto the machine by means of a fastener such as a bar (1.1), and the otherplates or semi-plates (2, 3, 4, 5, 6, 7) rotate on the plate itself (1),as is the case with the leg extension and leg curl machines where theresistance is fastened onto the mobile load arm (6.1), or else severalplates or semi-plates (2, 3, 4, 5, 6, 7) can be fastened to the machineand the plate (1) is left free to rotate on the latter as is the casewith the leg extension and leg curl machines where the resistance isfastened onto the rotation mechanism. 2 - Adjustable rotation radiusarticulated joint, as in claim 1, in which features just two plates (1,2) that is characterised by the facts that it is used on weight-liftingmachines and that it features one plate (1) that is bound with a fixingcomponent, such as a bar (1.1), to the machine itself and another plate(2) that is allowed to rotate freely onto plate (1) with reference toradius “c”, which passes through the femoral condyles of the seatedsubject (this second plate (2) features a mobile load arm (2.1) ontowhich the machine's resistance is assembled. 3 - Adjustable rotationradius articulated joint, as in claim 1, in which features just twoplates (1, 2) and which is characterised by the fact that it is used onweight-lifting machines in which the resistance is mounted onto the pin(1.2) in which the plate (2) is constrained to the machine and theresistance of the machine itself is transmitted to the mobile arm (1.1)by means of a (driving) shaft, whose longitudinal axis is placed on theextension of axis (c) of the knee; the other plate (1) constitutes theproximal part o the mobile arm (1.1); the said plate (1) features therectangualr central opening (2.2); the central pin (1.2) constitutes oneend of the propeller shaft, which features on the other end a featherkey (30) which is to be lodged in the central rectangular opening (2.2)of the plate (1); the pin (1.2)/propeller shaft features in proximity tothe feather key (30) a threaded area onto which a bolt or other stoppageis screwed; the central opening (2.2) is made longer verticallyaccording to the size of the feather key (30), whose point of symmetry(where the transverse and longitudinal axes meet) must coincide with theideal hole (2.4); the plate (2) is crossed by a cross-through hole (31)whose centre must correspond to the centre of the aforementioned idealhole (2.4), where the central pin (1.2)/propeller shaft will be placedand allowed to rotate freely; pin 1.3 is fastened to the plate (1). 4 -Adjustable rotation radius articulated joint, as in claims 1, 2 and 3,which is characterised by the fact that the plate featuring the pins(1.2, 1.3) can be both the one that is fastened to the weight-liftingmachine and the one that is free to move on this very plate. 5 -Adjustable rotation radius articulated joint, as in claims 1, 2, 3 and4, which is characterised by the fact that each plate (1 and 2) canfeature only one opening (2.2 or 2.3) and only one pin (1.2 or 1.3)provided that they alternate: thus, one plate (1 or 2) will feature oneopening (2.2 or 2.3) and the pin (1.3 or 1.2) that will be lodged in theopening (2.3 or 2.2) of the other plate (2 or 1). 6 - Adjustablerotation radius articulated joint, as in claims 1, 2, 3, 4 and 5, whichis characterised by the fact that the first (1.2) and/or the second(1.3) pin is joined to one or more elastic elements (such as a spring,rubber or other) placed directly on the ends of the respective opening(2.2 or 2.3); right angles to the rotation surfaces of the plates; thefirst pin (1.2), which can consist in one end of a propeller shaft, islocated in a central position and is inserted in the aforementionedcentral opening (2.2, 9); the second pin (1.3) is in a peripheralposition and is placed inside the peripheral opening (2.3, 10); theplates can move freely on one another with reference to the axis (c),which passes through the femoral condyles, when no plate is fastened toa fixed structure, as is the case with knee tutors and passivegymnastics machines; alternatively, a plate (1) can be fastened to themachine by means of a fastener such as a bar (1.1), and the other plates(2, 3, 4, 5, 6, 7) rotate on the plate itself (1), as is the case withthe leg extension and leg curl machines where the resistance is fastenedonto the mobile load arm (6.1), or else several plates (2, 3, 4, 5, 6,7) can be fastened to the machine and the plate (1) is left free torotate on the latter as is the case with the leg extension and leg curlmachines where the resistance is fastened onto the rotation mechanism.2 - Adjustable rotation radius articulated joint, as in claim 1, which,in its simplest form featuring only two plates (1, 2) with theresistance of the leg extension and leg curl applied directly to themobile load arm (2.1), is characterised by the fact that a plate (1) isconstrained to the machine by means of a fastener, such as a bar (1.1),while the other plate (2) is free to rotate onto the former plate (1)with reference to a horizontal axis “c”, which must correspond to theone that passes through the femoral condyles of the subject when seated;the plate (2) features a central opening (2.2) and a peripheral opening(2.3), while two pins (1.2, 1.3) are fastened to the other plate (1);the two pins (1.2, 1.3), located at a distance “I” are cross-throughpins and feature at the farther end a constraint which keep the plates(1, 2) from separating. 3 - Adjustable rotation radius articulatedjoint, as in claim 1, which in its simplest form features only twoplates (1, 2) with the resistance of the leg extension and leg curlapplied on the pin of the joint; the latter is characterised by the factthat the plate (2) is constrained to the machine and the resistance ofthe machine itself is transmitted to the mobile arm (1.1) by means of a(driving) shaft, whose longitudinal axis is placed on the extension ofaxis “c” of the knee; the other plate (1) constitutes the proximal parto the mobile arm (1.1); this plate features a central rectangularopening (2.2); the central pin (1.2) constitutes one end of thepropeller shaft, which features on the other end a feather key (30)which is to be lodged in the central rectangular opening (2.2) of theplate (1); the pin (1.2)/propeller shaft features in proximity to thefeather key (30) a threaded area onto which a bolt or other stoppage isscrewed; the central opening (2.2) is made longer vertically accordingto the size of the feather key (30), whose point of symmetry (where thetransverse and longitudinal axes meet) must coincide with the ideal hole(2.4); the plate (2) is crossed by a cross-through hole (31) whosecentre must correspond to the centre of the aforementioned ideal hole(2.4), where the central pin (1.2)/propeller shaft will be placed andallowed to rotate freely; pin 1.3 is fastened to the plate (1). 4 -Adjustable rotation radius articulated joint, as in claims 1, 2 and 3,which is characterised by the fact that the plate featuring the pins(1.2, 1.3) can be both the one that is fastened to the weight-liftingmachine and the one that is free to move on this very plate. 5 -Adjustable rotation radius articulated joint, as in claims 1, 2, 3 and4, which is characterised by the fact that each plate (1 and 2) canfeature only one opening (2.2 or 2.3) and only one pin (1.2 or 1.3)provided that they alternate: thus, one plate (1 or 2) will feature oneopening (2.2 or 2.3) and the pin (1.3 or 1.2) that will be lodged in theopening (2.3 or 2.2) of the other plate (2 or 1). 6 - Adjustablerotation radius articulated joint, as in claims 1, 2, 3, 4 and 5, whichis characterised by the fact that the first (1.2) and/or the second(1.3) pin is joined to one or more elastic elements (such as a spring,rubber or other) placed directly on the ends of the respective opening(2.2 or 2.3); these elastic organs can also be placed on the ends ofslits having the same longitudinal axis of symmetry of openings the (2.2or 2.3) and shorter than the diameter of the pins (1.2 and 1.3) insertedin the openings themselves (2.2 or 2.3). 7 - Adjustable rotation radiusarticulated joint, as in claim 1, which, when used with multipleplasters (4, 5, 6, 7) the latter are characterised by the fact that theyhave been cut according to an axis (e) which goes from the ideal pointof rotation (11) o the point where the radius (f) intersects with theouter edge; the said radius (f) is located in a position that isdiametrically opposite to radius “b”; these semi-plates (4, 5, 6, 7) arearranged in overlapping couples (4, 7 and 5, 6); their edges overlookinghave not been cut precisely along the axis (e), but rather, consideringthe aforementioned ideal point of rotation (11) to be the startingpoint, they diverge for a few degrees from axis (e) in the direction ofthe mobile arm (2.1, 6.1), or in the opposite direction, so that adistance is created between the two groups of semi-plates (4, 7, and 5,6) in correspondence with the intersection of axis (e) with radius “f”;this allows the rotation of one couple of semi-plates (4, 7) on theother (5, 6), with the aforementioned ideal point of rotation (11) asthe rotation fulcrum; by means of a screw (18), it is possible to adjustto the micrometer the distance between the two couple of semi-plates (4,7 and 5, 6); by means of screws inserted in the appropriate hole (3.2,5.1, 6.2), two overlapping semi-plates (5, 6) are steadily fastened tothe plate (3) which is located farther away from the other plate (1);semi-plate (4) is fastened to plate (3) by means of a pin (4.1), whichis to be lodged in a threaded hole (3.1) which is placed in theaforementioned ideal point of rotation (11), and is therefore free torotate with reference to semi-plate (5); semi-plate (7) is steadilyfastened to semi-plate (4) by means of a screw lodged in the appropriateholes (4.5, 7.1), consequently semi-plate (7) can rotate with referenceto semi-plate (6); as it is the spiralling part of the peripheralopening (10.2) is located on semi-plate (7), the ideal position of theperipheral opening can vary—owing to the rotation around the ideal pointof rotation (11)—with reference to the concentric part (10.1) of theperipheral opening itself; the said position can be adjusted by means ofthe aforementiond screw (18). 8 - Adjustable rotation radius articulatedjoint, as in claims 1 and 7, which is characterised by the fact that theperipheral opening (2.3, 10) can consist in an indentation, having thesame spiral shape of its cavity which faces the rotation surface of theother mechanical member. 9 - Adjustable rotation radius articulatedjoint, as in claim 1, 2, 7 and 8 which, when used with multiple plastersand with the resistance of the leg extension or leg curl machinesapplied directly to the articulated joint's mobile load arm (6.1), thearticulated joint is characterised by the fact that one plate (1) isfastened to the machine by means of a bar (1.1), while another plate (8)is in turn fastened to the plate (1) and acts as a cover; the other fiveplates or semi-plates (3, 4, 5, 6, 7) are connected to one another andare free to rotate between the plates (1, 8) that are locked withreference to a horizontal axis (c) which must correspond to the one thatruns through the femoral condyles of the subject when seated; plate (1)features two holes (1.4 and 1.5), one of which is located centrally(1.5) and the other peripherally (1.4) and at a distance equal to “I”from the first; a pin (1.2) is inserted in the central hole (1.5) andrests on central opening (9) of the overlooking semi-plate (6); anotherpin (1.3) is inserted in the second hole (1.4) and rests on peripheralopening (10) formed by the overlooking plates (6, 7). 10 - Adjustablerotation radius articulated joint, as in claim 1, 3, 7 and 8 which, whenused with multiple plasters and with the resistance of the machine isapplied to the rotation device, the articulated joint is characterisedby the fact that the plates (3, 5, 6) are fastened to the machines bymeans of a fastener, such as a bar, while plate (1) and a pin (1.2),which is located in the centre, which constitutes one end of a propellershaft, are free to move; plates (4, 7) are fixed to plate (3) and remainfastened to the machine but can rotate partially onto plates (5, 6)thanks to a pin (4.1) situated on the ideal point of rotation (11);plate (1) constitutes the proximal part of the mobile arm (1.1); insideit central rectangular opening (9) is made; the central pin(1.2)/propeller shaft features a feather key (30) which goes insidecentral rectangular opening 9 of plate (1); the said central pin(1.2)/propeller shaft features in proximity to feather key (30) athreaded area onto which a plate (8) is fastened, or a simple bolt whichacts as a cover for the entire system; plates (3, 5, 6) are crossed by across-through hole (31) whose centre must correspond to the centre ofthe previously mentioned ideal hole (9.1) inside which the central pin(1.2)/propeller shaft is lodged; another pin (1.3) fastened to plate (1)is lodged in inside peripheral opening (10). 11 - Adjustable rotationradius articulated joint, as in claims 1, 7, 8, 9 and 10, which ischaracterised by the fact that in the channel formed by the opening (9)it is possible to insert a spring (12) withheld by a distal spring-lock(13) which is perforated longitudinally and by a proximal spring-lock(14); the said proximal spring-lock (14) acts onto a bushing (15) withinwhich central pin the (1.2) is lodged, free to rotate onto the pin (1.2)and to slide inside the opening (9); proximal spring-lock (14) can bepushed by a peg (16), lodged in the mobile arm (6.1, 1.1) inside anindentation (17), the latter features two locking positions: when oneend of the peg (16) is inserted in the proximal locking position (17.1),bushing (15), pushed by the opposite end of the peg (16) itself (afterhaving crossed distal spring-lock (13)), is compelled to place itself onthe ideal hole (9.1), while when the peg (16) is inserted in the distallocking position (17.2), the bushing (15) is free to move inside theopening (9). 12 - Adjustable rotation radius articulated joint, as inclaim 1, 7, 8, 9, 10 and 11 which, when used with multiple plasters andwith the resistance of the machine is applied to the rotation device,both in the two plate version (1, 2) and in the multiple plate version(1, 3, 4, 5, 6, 7, 8), the articulated joint can be modified when thecentral pin (1.2)/propeller shaft is wider than the plate (1)/mobile arm(1.1); in this case the articulated joint is characterised by the factthat a guide is milled onto central pin (1.2)/propeller shaft and plate(1)/mobile arm (1.1) is placed inside the said guide; the ideal centralhole of the central opening of the plate (1)/mobile arm (1.1)corresponds to the centre of the central pin (1.2)/propeller shaft; thelatter features threaded hole; a three-part screw featuring head, bodyand thread, and whose threaded part is engaged in the threaded hole ofthe central pin(1.2)/propeller shaft, keeping plate (1) within theguide, with its non-threaded section going beyond the central opening;the head of the screw prevents the separation of the plate (1)/mobilearm (1.1) from the central pin (1.2)/propeller shaft; the plate (1) alsofeatures the peripheral hole (1.3) lodged in the peripheral opening ofthe overlooking plate. 13 - Adjustable rotation radius articulatedjoint, as in claim 1, characterised by the fact that the proximal partof the mobile arm (6.1, 1.1)features rectangular opening (19) which isengineered along the axis (a) wherein a screwed mechanical system (20)which permits it to move longitudinally along the opening (19) itself;onto this very mechanical system (20) the constraint to be used for theshins such as belt (21) will be fastened. 14 - Adjustable rotationradius articulated joint, as in claims 1 and 13, characterised by thefact that the mobile arm (6.1, 1.1) features a second rectangularopening (22) located distally, which is engineered along the axis (a)inside which a feather key (23) is lodged, free to slide along the axis(a) of the mobile arm (6.1, 1.1), and fastened to this very arm by meansof a pin (24); the foot rest is placed onto this feather key (23), thisfoot rest consists in a blade (25) or plate bent at one end by 90° or bytwo blades or plates fastened to one another at 90°; the vertical partof the foot rest allows the connection to the mobile arm (6.1, 1.1); thehorizontal part of the foot rest (25) allows the foot to rest and locksit by means of a constraint such as a belt (26). 15 - Adjustablerotation radius articulated joint, as in claims 1, 2, 3, 7, 9, and 10,characterised by the fact that on the outer edge of the plate (1) or onits periphery it features a degree angular scale (1.6) with the zeroposition corresponding to the longitudinal axis of the mobile arm (6.1,1.1) when the latter is the extension of the bar which joins the deviceto the machine or to the upper part of the knee tutor; the scale (1.6)develops in the opposite direction in which the peripheral opening (10)is developed; parallel to the distal opening (22) in the mobile arm(6.1, 1.1), on the outer edge or on the side opposite that to which theleg is fastened, a verification linear millimeter scale (27) is located,whose ideal zero is the ideal central hole of the plate (1). 16 -Adjustable rotation radius articulated joint, as in claim 15,characterised by the fact that instead of the degree scales (1.6, 27)two encoders may also be used to measure the movements simultaneously,one located in the place of the angular scale (27), the other in theplace of the linear scale (1.6) 17 - Adjustable rotation radiusarticulated joint, as in claims 1, 2, 3, 7, 9 and 10, characterised bythe fact that the pins (1.2, 1.3) inserted inside the central (1.5) andperipheral (1.4) openings can be ellipsoidal, in order to ease theirlongitudinal motion within the aforementioned openings (1.5, 1.4)); theymay also be provided with rolling bearings. 18 - Adjustable rotationradius articulated joint, as in claims 1, 7, 9 and 10, characterised bythe fact that the number of mobile plates between the locked plates canbe even greater, in order to divide the spiralling part (10.2) of theperipheral opening (10) into several areas, each one featuring its owncentre of rotation. 19 - Adjustable rotation radius articulated joint,as in claims 1, 7, 9 and 10, characterised by the fact that the plates(3, 5, 6) can consist in a single piece. 20 - Adjustable rotation radiusarticulated joint, as in the previous claims, characterised by the factthat the subject, in extending the leg, operates on the mobile arm (1.1,2.1, 6.1), compelling one plate to move with reference to the other(s)in the following manner. as the first part of the peripheral opening(2.3, 10) is shaped like a spiral going towards the centre of the plate(2, 6) and the distance between the two pins (1.2 and 1.3) is still “I”,in the first stage (the first 110-120°) one plate (2, 3, 4, 5, 6, 7)will be compelled to translate upwards and rotate onto the other plate(1) at the same time, thereby causing the mobile arm (1.1, 2.1, 6.1) todo the same; as the other part of the opening (2.3, 10) is acircumference with a centre that coincides with that of the ideal hole(2.4, 9.1), subsequently (the remaining 15-25°) the plates will simplyrotate onto one another; when the leg is flexed the same motions willoccur but reversed. 21 - Adjustable rotation radius articulated joint,as in the previous claims, characterised by the fact that it may also beused as an accessory in combination with the traditional mechanism,thereby making the machine more functional; lastly, the articulatedjoint may also be used as an accessory on other types of machines (orseats) endowing them with the same functions as the leg extension andleg curl machines; in the latter case, the fastening bar will be lockedto the machine (or simply to the seat) by means of those components thatare known to achieve this aim.